During the previous years of this proposal studies concentrated on the spinal cord circuitry through which nociceptive inputs are transmitted. In the present proposal the investigators will take a multidisciplinary approach to the mechanisms through which SP/NKA contributes to the transmission and nociceptive messages, including analysis of the second messenger systems through which the long term changes are induced in the site of injury. In Specific Aim I they will use an in vivo electrophysiological approach to address the hypothesis that the phenotype of the PPT-A mutant mice involves changes that occur at the level of the spinal cord dorsal horn. In Specific Aim II they will address the selective contributions of SP and NKA to nociceptive processing, by generating and studying mice with the lesions of either SP or NKA. Phenotype of these mice will be tested with anatomical behavioral and electrophysiological approaches. In Specific Aim III we will examine downstream second messenger consequences of primary afferent, SP/NKA mediated nociceptive inputs. We will examine the interaction between SP/NKA and calcium dependent second messenger systems, by evaluating the extent which PKC and alpha calcium calmodulin kinase II are altered by injury in wild type and PPTA mutant mice. Finally in Specific Aim IV they will focus directly on the contribution of alpha calcium calmodulin kinase II to tissue nerve injury induced pain states by studying mice with alterations in the gene that codes alpha calcium calmodulin kinase II. Taken together, these studies will provide important new information that can be used to develop new therapeutic approaches to treat persistent pain conditions.